Tracing is what you include in your code so you know what’s happening during development and more importantly in production. Supporting players like .NET and the operating system also have trace output.

ETW stands for Event Tracing for Windows and is the tracing mechanism built into the Windows operating system.

.NET provides good ETW support starting with .NET 4.5 with the EventSource class. This creates an ETW provider. You need external tools (not yet available in Visual Studio) to create and view traces.

ETW tracing with the EventSource class is fundamentally different than Trace and TraceSource. It is a different pipeline, configured with ETW tools, and can be turned on and/off without restarting your app.

ETW does the slow part of tracing on a separate thread. Trace, TraceSource, Log4Net and most other trace solutions do not do this, or not with the massive efficiency and blazingly fast performance of ETW.

Semantic tracing logically decouples from trace technology, isolates trace decisions like severity, is strongly typed (at the app), and states what is happening in the app, not details of what the trace should say.

Semantic tracing can be done with any trace technology, allowing you to switch later to ETW if you can’t do it now.

The Semantic Logging Application Block (SLAB from P&P) uses EventSource, avoids ETW tools during development, eases the transition to ETW, and has docs on using a semantic approach to tracing.